Of all the moments captured for eternity in bronze, few are as stirring as when Col. Robert Gould Shaw led the 54th Massachusetts Regiment, the first regiment of African-American soldiers in the U.S. Army, out of Boston. The date was May 28, 1863, and it turned out to be a watershed moment, both in the Civil War and in American history.

As depicted by Augustus Saint-Gaudens, the American Renaissance sculptor who spent his final years in Cornish, the beginning of that long march from Boston Common to the battlefields in the South foretells its ending: Shaw was killed leading his men into battle in South Carolina not quite two months later. For the Robert Gould Shaw Memorial, Saint-Gaudens placed the colonel astride a horse, sword drawn, riding alongside his men. The soldiers’ torsos lean forward and their faces wear expressions of placid determination. They are fighting not only for the Union but for their own equality.

The memorial was installed on Boston Common in 1897 and immediately drew accolades. “How I rejoice that something really fine is to stand there forever for R.G.S. and all the rest of them,” Henry James wrote. “This thing of Saint-Gaudens strikes me as real perfection.” It is now widely considered Saint-Gaudens’ finest work.

But the memorial had a life beyond its installation. Saint-Gaudens kept tinkering with a plaster model of it, changing small details. Through a long series of events, a new bronze casting of the artist’s masterwork was placed at the Saint-Gaudens National Historic Site in Cornish in 1997.

On Thursday, the 150th anniversary of Shaw’s death, the Saint-Gaudens site will kick off a series of events commemorating Shaw and the memorial. In addition to reminding the Twin States of the masterwork in their midst, the events promise to shed a welcome light on Shaw, who was justly celebrated in his time, and Saint-Gaudens, who until recent years had been among the country’s most under-appreciated artists.

The two men share a story, of initial discomfort with people of whom they knew little, African-Americans who were assimilating, haltingly, into mainstream life.

Although his well-to-do Boston parents were ardent abolitionists, Shaw was initially reluctant to lead the 54th Regiment. He had served with some distinction after joining the Union army in 1861 and was concerned that leading the black soldiers might hurt his career, said Henry Duffy, curator at the Saint-Gaudens site.

Shaw, then only 25, also worried about whether he was good enough to lead the regiment, Duffy said. A clause in the Emancipation Proclamation, signed by President Lincoln on Jan. 1, 1863, enabled black soldiers to join Union forces, and under the urging of Frederick Douglass, men poured into New England from far and wide.

But Shaw had good reason to be apprehensive. After the proclamation, the Confederacy declared that any black Union soldier would be hanged, and that any officer leading black troops would not be afforded the customary fair treatment in enemy hands.

Shaw’s mother persuaded him that he was the right man to lead the 54th Regiment into battle, which he did, after a few minor skirmishes, on July 18, 1863 at Fort Wagner, in Charleston, S.C. Shaw and his troops led the charge and at the top of the fort’s earthen ramparts, where he was shot and killed.

As a presumed insult, Confederate General Johnson Hagood buried Shaw’s body with those of his dead troops. Shaw’s father declined to seek his son’s body for reinterment, declaring, “We would not have his body removed from where it lies surrounded by his brave and devoted soldiers. ...We can imagine no holier place than that in which he lies, among his brave and devoted followers, nor wish for him better company — what a body-guard he has!”

The regiment had 272 casualties at Fort Wagner, including as many as 62 soldiers killed, but was heralded for its bravery, which led to more African-American enlistees. Lincoln later said that this rush of enlistment was a decisive factor in the Union victory. The Union’s loss at Fort Wagner resulted in a long siege, which ended with the fort’s abandonment in September 1863.

Almost immediately after the battle, a call went up for a monument to Shaw. A proposal to memorialize him where he fell was short-lived, owing to Southern hostility and poor soil at the site.

Saint-Gaudens received the commission to make the Shaw memorial in 1883. Shaw’s family encouraged the artist to depict him with his men. Saint-Gaudens set to work in New York, choosing African-American men off the street and paying them a quarter apiece to pose for him. In all, he made 40 plaster studies.

It was during this process that Saint-Gaudens’ experience dovetailed with Shaw’s, Duffy said. The artist was already among the country’s preeminent sculptors, and although he was from a working class family he lived in a rarefied world, working primarily for the corporate barons of the Gilded Age. His portrait sessions, which often stretched for a couple of weeks, plunged Saint-Gaudens into a world he barely knew.

“He would have had a period there where he would have been introduced to the fact that hey, these are just guys,” Duffy said.

Saint-Gaudens worked on the Shaw Memorial for 14 years, long enough that many of the veterans were dying off. The group that commissioned it “had to kind of drag it out of him,” Duffy said.

The finished work, complete with a frame designed by architect Charles McKim, a frequent collaborator of Saint-Gaudens’, was installed on the common, across Beacon Street from the Statehouse. The dedication on May 31, 1897 was a moving event, as Saint-Gaudens described it.

“Many of them were bent and crippled, many with white heads, some with bouquets... The impression of those old soldiers, passing the very spot where they left for the war so many years before, thrills me even as I write these words. They faced and saluted the relief, with the music playing John Brown’s Body. ... They seemed as if returning from the war, the troops of bronze marching in the opposite direction, the direction in which they had left for the front, and the young men there represented now showing these veterans the vigor and hope of youth. It was a consecration.”

But Saint-Gaudens wasn’t done with his masterpiece. Even after 14 years of work, he continued to refine the memorial, making small changes to the way Shaw held his sword and to the rifles and flags carried by the soldiers, among other details. A full-scale plaster cast traveled to Paris, where Saint-Gaudens had studied years before, for exhibition in 1900, then to Buffalo, N.Y., where it was exhibited at the Albright-Knox Museum as part of the Pan American Exposition.

After the exhibition in Buffalo ended, the plaster memorial fell into limbo. It was too cumbersome to move, so the museum built a wall in front of it. It remained there until 1947, when the wall was taken down. Museum officials contacted the artist’s son, Homer Saint-Gaudens. He put it in the hands of the Saint-Gaudens Memorial, which maintained the Cornish home and grounds from 1919 until 1964, when it was given to the government as a park. The plaster cast remained in Cornish until the mid-1990s. It was used as the basis for the bronze casting in 1997, then loaned to the National Gallery of Art in Washington, D.C., where it remains.

In Cornish, the bronze memorial was placed at the end of an enclosure that was once a bowling lawn, surrounded by hedges of hemlock and pine. It towers over visitors, but not as grandly as other Saint-Gaudens works. The figures, which are rendered in a mix of high- and low-relief, are more or less life-size. The ranks of troops are pressed together, distilled to their essential details — boots, uniforms, bristling rifles and, most importantly, their faces. The drape of the men’s trousers, the seams along the bottoms of their canteens, the jackets flapping gently, the intent look on the faces, all of these give the work a feeling of movement toward a shared destiny.

Above Shaw and the two dozen or so soldiers floats an angel bearing olive branches, symbolizing peace, and poppies, symbolizing death. “It lifts the piece up into the spiritual realm,” Duffy said.

The memorial is inscribed with the Latin phrase “Omniare Relinquit Servare Republicam,” or “He gave all in the service of the republic.” A brief, inaccurate description scrolls across the base of the monument in capital letters: “Robert Gould Shaw, killed while leading the assault on Fort Wagner, July Twenty Third, Eighteen Hundred and Sixth Three.” Why the artist got the date wrong is unknown, Duffy said.

Elsewhere, the details are accurate, even where the viewer can’t see them. The memorial is due for a cleaning, Duffy said, a yearly event that gives the workers on their scaffolding a view of the braids on top of Shaw’s hat, and of the fully realized soldiers out of view behind Shaw’s horse.

With so much public sculpture bearing his stamp, Saint-Gaudens was never exactly forgotten. But with the advent of modernism and its many offshoots, his mixture of grit and grace receded into the background. The reopening a few years ago of the Metropolitan Museum of Art’s American Wing situated Saint-Gaudens at the heart of the nation’s art history. The Met mounted an exhibition of its holdings of Saint-Gaudens’ work that resulted in a fresh wave of acclaim. The New Yorker art critic Peter Schjeldahl, upon visiting the Cornish park, called the Shaw Memorial Saint-Gaudens’ “most powerful achievement.”

“The shared expression of the many faces harrows,” Schjeldahl wrote of the memorial. “It strikes me as the courage, indistinguishable from indifference, of the already dead.”

The historian David McCullough, who gave a talk at the Saint-Gaudens site while researching his 2011 book The Greater Journey: Americans in Paris, said that every American ought to see the Shaw Memorial.

About 30,000 people come to the artist’s former Cornish home every year, Duffy said, a number that has been on the rise in recent years. Even so, on a weekday afternoon it’s possible to have a one-on-one conversation with one of the greatest works of American art.

“The thing that we have that you don’t get in Boston is quiet,” Duffy said.

This summer’s events surrounding the memorial could change that a bit. The exhibition opening reception is on Thursday from 5 to 6 p.m., and includes remarks from Duffy. The site’s Picture Gallery will house period rifles, some of Saint-Gaudens’ preparatory sketches and relics related to a Cornish native who met the same fate as Shaw. Col. Haldimand Putnam led the New Hampshire 7th Regiment against Fort Wagner, just behind Shaw and his troops. A Confederate officer who had been Putnam’s classmate at West Point cut Putnam’s epaulets from his uniform and sent them back to New Hampshire so the dead man could be identified. The epaulets will be part of the exhibit, Duffy said.

The exhibit remains on view through Sept. 9. On Aug. 10, the park will hold a special daylong celebration that will feature the Massachusetts 54th Regiment Re-enacters, demonstrations of period weapons, and a talk by David Blight, the Class of 1954 Professor of American History at Yale University, on the subject of “The Shaw Memorial and the Aftermath of the Civil War.”

The Boston African American Museum and the National Gallery of Art will hold events with their Shaw Memorials later in the year.

The Aug. 10 events in Cornish include a commemoration of the memorial. But the historic site is open from Memorial Day through the end of October, which makes this moment of American history available for months at a time.

Alex Hanson can be reached at ahanson@vnews.com or 603-727-3219.

CLARIFICATION

This article has been amended for clarification. The Massachusetts 54th Regiment had 272 casualties in the Civil War battle at Fort Wagner, S.C., including as many as 62 soldiers killed. Those figures were unclear in an earlier version of this story.